The present invention is generally related to storage systems. More particularly, the invention is directed to a disk-based storage system, which provides one or more back-end virtual vaults to one or more front-end visible virtual or physical tape libraries.
In physical or virtual tape libraries, users often purchase a relatively small tape library and license their backup application code for the relatively small tape library due to the tremendous expense associated with large tape libraries. Referring to FIG. 1, a typical small tape library 10 comprises a plurality of media slots 12 and one or more tape drives 14. The tape library 10 keeps track of all of the tapes in the media slots 12 and the tape drives 14, and provides overall management of the tapes. When a user desires to read from or write to a tape, the tape is removed from a media slot 12 and placed into the tape drive 14. Of course, the tapes 16 do not reside within the tape library 10 in perpetuity. Accordingly, tapes 16 may be removed from the tape library 10 to become external tapes 18. These external tapes are typically stored offsite for security or archiving purposes. External tapes 18 may also be imported into the tape library 10 as desired as long as there are enough media slots 12 available.
Although having a small tape library 10 is an inexpensive way, (in terms of hardware), for an organization to implement data storage using tapes, it is a relatively labor intensive environment. Since the tape library is small, the user is forced to continuously import and export tapes to and from the tape library 10 so that needed tapes can be utilized by the tape drive 14.
To alleviate the labor problem, a larger tape library may be used. Such a larger tape library is shown in FIG. 2. In this large tape library 20, 166 media slots 12 are provided. Although only two tape drives 14 are shown for simplicity, those skilled in the art would realize that more tape drives 14 would typically be provided for a tape library of this size unless the system is used exclusively for archiving purposes. As one could obviously deduce, having such a large tape library 20 would relieve the user from having to import and export tapes on a frequent basis.
However, large tape libraries 20 have the drawback that they are much more expensive in terms of the hardware and, equally importantly, the library software license.
A seemingly unrelated problem is the desire of physical tape library vendors to include a virtual tape library as a relatively small front-end cache. In order to do this, the virtual tape library cache must be able to track tapes that have been exported to a physical tape library and import the appropriate tapes whenever the data protection application (DPA) needs access to tapes that are not located within the virtual library. Unfortunately, the DPA cannot distinguish between tapes that have been completely exported and shipped off-site and tapes that have simply been moved electronically or robotically to a back-end vault.
Thus, the problem of importing and exporting tapes to and from a tape library is closely related to the problem of designing a small front-end cache to a large library. This is because much of the work in designing such a cache involves moving media between the front-end cache and the backend vault, effectively exporting media from one library and importing this media into the other and keeping track of this interaction.
Accordingly, present tape library configurations leave much to be desired in terms of flexible import/export mechanisms; particularly when media is moved between multiple libraries.